A generic process is known from DE 37 20 684 A1 in which the combustion enthalpy that occurs in the unprocessed exhaust gas during the after burning of nonburned fuel components is measured. A lambda sensor is arranged behind the heated catalytic converter unit and is linked to the heat regulation system of the catalytic converter. A reference calorific output that occurs when air flows through the system is placed in relation to the reduced calorific output that occurs when combustible exhaust gas components are converted in the catalytic converter unit. Although this process measures the total percentage of nonburned components in the exhaust gas, information on the temperature of the catalytic converter can only be indirectly inferred from the calorific output. The lambda sensor is also used to determine the air-to-fuel ratio. This process can be used to characterize the combustion behavior of the engine.
A process for the protection of catalytic converters used in exhaust gas cleaning is known from DE 40 20 383 A1 in which a heat tone sensor is positioned upstream from the catalytic converter in the exhaust gas flow. The heat tone sensor consists of a resistive temperature sensor with a catalytically active coating. Because the same exothermic reactions take place at this heat tone sensor as in the downstream catalytic converter, this information can be used to determine the percentage of nonburned exhaust gas components. The temperature of the exhaust gas or of the catalytic converter can be measured with a second temperature sensor without a catalytically active coating. The process according to DE 40 20 383 A1 cannot be applied to selectively measure individual exhaust gas components.
The objective of this invention is to provide a process for monitoring the operativeness of a catalytic converter which provides information on both the percentage of individual non-converted exhaust gas components, as well as on the current thermal load on the catalytic converter.